The present invention relates to an adjustable armrest of an office chair, and more particularly to such an adjustable armrest which comprises an armrest coupled to a bottom plate on an armrest holder frame through two pivoted movable plates, and lock means adapted to lock the armrest in a received manner.
Regular office chairs are commonly equipped with fixed armrests for resting the arms. However, these fixed armrests cannot be adjusted to different positions as desired. FIGS. 1 and 2 show an adjustable armrest structure for office chairs. This adjustable armrest structure comprises a bottom plate 11 fixedly mounted on an armrest holder frame 1, a first movable plate 12 pivoted to one end of the bottom plate 11 by a pivot and axle bearing unit 17, a second movable plate 13 pivoted to one end of the first movable plate 12 remote from the bottom plate 11 by a pivot and axle bearing unit 16, and an armrest pad 14 having two downward parallel lugs 15 bilaterally pivoted to the second movable plate 13. The bottom plate 11, the first movable plate 12 and the second movable plate 13 have a respective locating hole 111; 121; 131. When the armrest is received in a received condition as shown in FIG. 2, a lock pin 18 is fastened to the locating holes 111; 121; 131 to fix the bottom plate 11, the first movable plate 12 and the second movable plate 13 in a stack. This structure of adjustable armrest has drawbacks. Because the axle bearings of the pivot and axle bearing units 16; 17 are ball bearings, the first movable plate 12 and the second movable plate 13 tend to be forced away from the received position to the extended position, therefore the operator's hands tend to be jammed in parts of the adjustable armrest. Another drawback of this structure of adjustable armrest is that the complicated locking procedure of aligning the locating holes 111; 121; 131 and fastening the lock pin 18 to the locating holes 111; 121; 131. Still another drawback of this structure of adjustable armrest is that the lock pin 18 tends to fall from the locating holes 111; 121; 131, thereby causing the adjustable armrest to be unlocked. Furthermore, when the user inserts the fingers into the gaps between the armrest pad 14 and the second movable plate 13, the fingers may be jammed and injured.